the packages are stored in the [msdb].[dbo].[sysdtspackages90] table. The source xml of the package is stored in the [packagedata] column as image.
If you want to see the source XML of the package, you can simply convert it by simple select.
,CONVERT(xml, CONVERT(varbinary(max), [packagedata])) as XMLPackageData
If you store the content of the XMLPackageData into .dtsx file, you have the original package.
If you make a backup of your msdb database and restore it under other name, you will not see the packages on the server as the packages are being red from msdb. You can access them by the above mentioned query with appropriate database name